There are more than 400 commercial nuclear power reactors worldwide. Over 90% of these nuclear reactors use fuel which is composed almost entirely of uranium dioxide (UO.sub.2). During irradiation, elements not found in the fresh fuel are produced within the fuel as a result of fission of the uranium atom nuclei. Many of these newly generated radionuclides emit radiation which is extremely hazardous to humans. Such spent nuclear fuel from commercial power reactors constitutes the bulk of high-level nuclear waste (HLW). Selective removal of these hazardous radionuclides from the spent fuel is difficult, expensive, and, in some countries, is prohibited by government regulations. Most countries have specified that after removal from the reactor, spent nuclear fuel shall ultimately be disposed of in geologic repositories that are deep, mined cavities in stable geologic formations. These geologic repositories will isolate the hazardous radionuclides from the accessible environment. Such laws ensure the health and safety of the public (See, e.g., the United States Nuclear Waste Policy Act of 1982, as amended, 42 U.S.C. .sctn.10101.)
During the long time periods (i.e., thousands to millions of years) envisioned for disposal in geologic repositories, spent fuel may come in contact with groundwater. Laboratory experiments, however, show that spent fuel is readily oxidized and dissolved by many common groundwaters. Dissolution of the spent fuel presents an unacceptable risk of releasing the previously sequestered hazardous radionuclides into the groundwater. This is because, upon release into the groundwaters, the hazardous radionuclides may be transported to the accessible environment. This poses a serious threat to public health and safety.
At present, electric utilities that produce power from nuclear reactors do not directly address these problems. In the conventional nuclear fuel engineering sequence, fuel for nuclear power reactors is fabricated, irradiated, and then removed from the reactor to be temporarily stored prior to final disposal in a geologic repository. Each step of the sequence is engineered to optimize power production characteristics and to provide for safe operation and handling of the fuel during power production and storage. Over the past three decades, significant improvements have been made to the nuclear fuel engineering sequence to optimize fuel costs and performance. However, no part of the fuel engineering sequence is designed to enhance fuel material attributes that improve the retention of hazardous fission products within the spent fuel that a geologic repository may hold.
In light of the above, the safe, long-term retention of hazardous radionuclides within a spent fuel geologic repository is a high priority need for commercial nuclear power producers in numerous countries world-wide, including the United States. Important technical design aspects of these repositories have been the subject of intense interest and research world-wide for many years. Nevertheless, one of the critical design aspects that remains to be decided is the character or material attributes of the spent fuel to be stored in the geologic repositories. At a minimum and in light of the above, the character of spent nuclear fuel must be engineered so that the spent fuel retains the hazardous radionuclides and prevents them from entering groundwater systems, as well as satisfies legal restrictions that control spent fuel reprocessing.
Accordingly, there is a need for a method that properly prepares spent nuclear fuel for disposal in deep geologic formations so as to avoid oxidation and dissolution of hazardous radionuclides in groundwater.
There is a further need for a method that economically prepares spent nuclear fuel for long-term storage without affecting the operation and utility of existing and planned nuclear power plants.